The present invention generally relates to power converters, and more particularly to power converters that are utilized to charge lead-acid batteries, still more particularly to a control module that selectively and/or adaptively changes the magnitude of the power converter's output voltage such that sulfation of a lead-acid battery is avoided and/or reduced.
Power converters for converting AC power to a regulated DC level are well-known and frequently utilized to charge lead-acid batteries. Low-cost power converters typically comprise a rectifier and DC voltage regulator. These power converters typically fix the power converter's output voltage at some pre-determined level based on an optimum or standard operating and/or storage condition. The output voltage of these power converters is typically subject to substantial variation and instability, which leads to overcharge and/or undercharge of attached lead-acid batteries. Undercharging and/or overcharging a lead-acid battery normally shortens its operating life and causes reduced performance.
Increasing a power converter's output voltage aids in preventing electrolyte stratification and can reduce sulfation, thus extending both the life and capacity of the battery. On the other hand, decreasing the power converter's output voltage can reduce water boil-off which typically reduces maintenance and extends the battery's operating life.
Typical lead-acid batteries include lead/lead dioxide plates submerged in sulfuric acid. These plates are formed into cells which normally produce around 2 volts. A typical 12 volt battery includes six 2 volt cells. As a battery discharges, a chemical reaction transforms lead dioxide to lead sulfate. Lead sulfate acts as an insulator and decreases current flow through the battery. Additionally, the build-up of lead sulfate on a battery's plates causes a drop in the battery's output voltage. When a lead-acid battery is not in use it slowly self-discharges. This self-discharge also leads to sulfate build-up on the battery's plates. When the lead-acid battery is recharged the lead sulfate is normally converted back to lead dioxide. However, when a battery is left in a discharged state for an extended period, the lead sulfate hardens and the battery becomes more difficult to charge. This, in turn, leads to increased lead sulfate build-up until the battery becomes useless.